E36 sub woofer placement

Hi All. I'm looking for a good sub woofer arrangement for my 1996 328Is.
Here's what I have now (it doesn't sound very good). 2 Nakamichi 8 inch in a
cheap, but solid box. It looks like many that you see. Nothing special. My
car doesn't have a pass through but both seats can fold inward. If I had a
pass through, my problem would be solved (I would place the sub here) and I
don't want to drive around with one seat folded. The trunk area is very well
sealed from the cab and here lies the problem: I have to turn the subs WAY
high to have a noticeable increase in bass. Plus I think the relatively
large amount of air being moved is having an adverse effect on the 6x9s in
the rear deck. With other cars I've had in the past, a single sub mounted on
the rear deck between the two 6x9s has worked well for me. I think this
arrangement would work well for me. I noticed that there is some structural
reinforcement here but I have a friend who is a race-car chassis builder and
could tidy things up for me. If you have a sub arrangement in your E36 that
you really like, I'd be interested in hearing from you. TIA

Chris